(2) All motor oils contain additives designed to hold moisture (water vapor) in suspension within the oil to keep it from separating so that it can be vaporized by the heat of use. Without that heat, the additives will continue to absorb and hold moisture against the gun metal.

In these (modern) days of advanced technology, when there are hundreds of specialized lubricants and corrosion preventers available for us to use in every conceivable situation, why so many of us continue to try to use an oil formulated for one particular application for another, completely different application, is beyond human comprehension.

Earl, while you want to know why you should not use motor oil on your gun, I'd have to ask "Why would you want to?"

"If you have a lot of oily rags lying around your garage, it makes sense to do something with them other then throw them in the trash."
Sorry. Throwing oily rags in the trash makes the MOST sense to me....certainly much more sense than wiping your shotgun down with dirty/oily rags that you find laying around your garage....... tsk, tsk, tsk...
Spend $4 on some gun oil and clean up your abode!

Earl.... Looks like I'm in the minority here. I use ONLY 30w motor oil to lubricate, and protect, my gun. I have never seen any type of lubricant that did not attract dust or dirt. It's the very nature of the product. I can see absolutely no difference between wiping a gun down with, say, Remington Gun Oil, than I do with wiping it down with 30W motor oil on a soft rag. It has worked on my gun for years with no ill effects. I prefer to lubricate the gun with 30W motor oil, and wipe the entire gun down, metal, wood, and all, with a soft cloth sprayed liberally with Scotts Liquid Gold furniture polish. It really gives the gun a nice protective coating and looks great.......Just my experience....Dan Thome (Trap2)

The Perazzi book by Karl Lippard says to use 30 weight non-detergent motor oil. A P-gun is like any other when it comes to oil. You don't want to use a mix oil because it's high detergent -- has additives that could harm your gun.

Motor oil is formulated to withstand very high heat, very high pressures, lots of acids and combustion byproducts, not foam, and to lubricate and carry off heat while not loosing excessive viscosity, and not deal with much moisture.

Gun oil has to withstand none of the above. Instead it has to lubricate a little, displace some moisture and be a good corrosion preventative.

Lubricating under harsh conditions vs. prevent corrosion under relatively benign conditions. Two very different attributes that require two very different oils. Might as well use the oil designed for the job at hand.

As BigAl said, you wouldn't put gun oil in your GMC....why would you put motor oil on your gun?

Earl4140- One US manufacturer of excellent trap uses and recommends non detergent motor oil for his guns. You asked about wiping down the outside of the gun. The purpose of wiping down the outside of the gun is to protect against rust. Motor oil will work fine for this. I prefer a grease for the inside parts.

In all the years of shooting and building guncases I have had three problems with lubricant on a gun,, and then stored in one of my cases. This involved Rem-oil by Remington,, excessive heat,, and sunlght directly thru rear window onto the case. upwards of 110 degrees in the car. Rem-oil has Teflon in it!,, that is the culprit. It softened the finish on the gun and it suck to the velvet interior of the case. Haven't been able to duplicate the problem with any other product.

SO,, I say to you,,, don't use Rem-oil in a high temp situation!!
Other than that,,It really don't matter what you use!! Just so you use something. Paul

"Capt, can you name and oil or grease that repels dust and dirt? I think no oil or grease "attracts" dust and dirt. The dust and dirt simply lands on something and sticks."

Some of you guys are as bad as my wife! Geeez! She takes everything I say so literally that even when I just say "Yes, dear!" She immediately comes back with something like "and just what is that supposed to mean, exactly?" Forget I said anything. I can get all the abuse I can digest without wasting electricity to do it!

"Just so you use something" Good point, Paul. Lubrication of guns isn't exactly high tech. After all, they aren't jet ingines opearting at red hot temps and 100,000 rpm. Keep 'em wiped down so they don't rust, and lightly oiled or greased at wear points, and they'll last a long time.

The best product on the market is a spray on product called "Plexus". I was told about this at a shoot from a new friend of mine. This product is outstanding!!!! I bought a case of it because I was so impressed with the results. You can spray it on the barrels and on the stock and fore arm, wipe it off with s soft rag, and what a shine too both the metal and the stock!
It repels water like rain X and protects your gun in rain or snow. The product was designed for Jet Aircraft canopies, and it works on any painted surface also. If you have a motorcycle, use it on the windshield if you have one.
Buy one can, just try it, then you decide.

My other 2 cent's worth, do not use motor oil on any gun. Motor oil was designed for engines, not firearms.

Not only will motor oil work as a lubricant and rust preventative, but good ol' clean diesel oil is a great solvent to clean shotgun actions with. It cleans away grime and grit and leaves a slight coating on the metal surfaces which help repel water. The issue with diesel is that it has a higher toxicity that some more highly refined "fit for purpose" oils. But if you avoid contact with the skin (use latex gloves), use protective eyewear (which you should anytime you're cleaning with solvents), and use in a well ventilated area, you're good to go!